The present invention relates to a scroll type fluid machinery, which can be used as compressors, vacuum pumps, expansionary machines, etc.
A regular scroll type fluid machinery usually consists of a casing, a stationary scroll fixed on the casing, a driving crankshaft rotatably supported on the casing with bearings, and an orbiting scroll driven by the crankshaft. The orbiting scroll is constrained by an anti-self-rotating mechanism to realize an orbiting movement with respect to the stationary scroll. The volumes formed between the stationary scroll and the orbiting scroll change with the orbiting movement of the orbiting scroll, and the changing volumes compress the fluid in the volumes. The thrust force generated by the fluid pressure exerts on the orbiting scroll, and passes to a thrust bearing.
In order to reduce the energy consumed by the friction force on the thrust bearing, a double orbiting scroll structure was proposed. These two orbiting scrolls are mounted back-to-back to cancel the thrust force. This structure has been described in U.S. Pat. Nos. 801,812, 3,011,694, and 4,990,071.
There are two approaches for providing the driving force in the aforementioned patents. One approach is to make the driving shaft shun the stationary scroll and to input the driving force through some driving mechanisms surrounding the periphery of the orbiting scroll. The other approach is to make the crankshaft go through the center of the stationary scroll to drive the back-to-back orbiting scrolls.
The first approach greatly increases the size of the machine because the driving shaft must be mounted on the outside surrounding the stationary scroll. The second approach reduces the volume compression ratio of the fluid machinery because the driving device occupies the central portion of the orbiting scroll, which is vitally important to the compression ratio.
Another structure used to cancel the thrust force can be found in U.S. Pat. Nos. 4,515,539 and 6,267,572B1, and Japanese Patent Document 04-121,474. Two mirror-imaged orbiting scrolls are connected to the two ends of a thrust-canceling shaft, which is rotatably fitted into an eccentric through-hole in a motor shaft. To prevent the orbiting scroll from self-rotation, a mechanism is specially provided. Furthermore, the relatively weak stiffness of the orbiting scroll is caused by the fact that the orbiting scroll is supported by only one thrust canceling shaft, thus affecting the efficiency of the compressors.